The invention relates to a device for controlling the air flow of a supercharged internal- combustion engine with a supercharger to deliver charge air from a suction line located upstream of the supercharger through a charge air line located downstream of the supercharger to the internal combustion engine, with the suction line comprising an intake and a recirculating line including a recirculating valve being located between the charge air line and the suction line, and with the recirculating line between the recirculating valve and the suction line being formed by a line section that terminates downstream of the intake in the suction line of the supercharger
A device for controlling the air flow of a supercharged internal combustion engine of the above-mentioned general type is already known from German Patent Document DE 35 06 235 A1. The device comprises a supercharger to deliver charge air from a suction line located upstream of the supercharger through a charging air line located downstream of the supercharger to the internal combustion engine, with the suction line comprising an intake and a recirculation line with a recirculating valve being provided between the charge air line and the suction line. The recirculating line is composed of a line section between the recirculating valve and the suction line, said section terminating downstream of the intake in the suction line of the supercharger.
Reference is made to German Patent Documents DE-OS 20 27 883 and DE 29 33 556 C2 for general technical background.
One disadvantage of devices of the general type referred to above is their relatively high induction noise level. Although the noise generated by the flow deflection at the intake itself is usually sharply reduced by a flow-favorable design of the intake, in mechanically supercharged internal combustion engines for example an unsatisfactorily high induction noise remains, produced primarily by pressure pulsations on the intake side of the supercharger.
The invention is based on the object of designing a device of the above-mentioned type in such fashion that a considerable reduction of the induction noise can be achieved.
This goal is achieved according to the invention by providing an arrangement wherein, in order to reduce induction noise, a length of line section from the recirculating valve to the opening in the suction line is dimensioned so that the line section with the recirculating valve closed forms a resonator that is tuned to one or more pulsation frequencies of the supercharger.
One advantage of the device according to the invention consists in the fact that a significant reduction of the induction noise is achieved by adjusting the length of the line section, which depends on a pulsation frequency of the supercharger, from the recirculating valve to the opening into the intake line in such fashion that the line section, with the recirculating valve closed, forms a resonator tuned to one or more pulsation frequencies. Thus, during full-load operation, the recirculating valve is completely closed. The total air volume is drawn through the intake in the air filter. The line section thus constitutes a closed connection to the recirculating valve and, by adjusting the length of the line section to the pulsation frequency of the supercharger, an effect is obtained such that the line section acts as a bypass resonator that sharply dampens the pulsations of the supercharger.
With a partially or completely closed recirculating valve, the line section no longer acts as a resonator but as an induction noise damper. As a result, a much improved reduction of the induction noise is achieved by the device according to the invention even during partial load operation, with the recirculating valve partially or completely open.
In preferred embodiments of the invention the recirculating line and recirculating valve are supported in a filter housing which also houses the intake end of the intake line.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.